HCS12. Address space of external devices in expanded wide mode?

After reading the app note on accessing external devices, another thing that troubles me is the address space when using expanded wide mode. For me it looks like that when using the expanded wide mode all addresses from 0x4000 to 0xFFFF is taken from outside? Including the vector area? Is this really true?

I only need to attach a 16bit wide DAC to my design… so I only need a very small address space for that. 4 – 16bit addresses actually. Is it possible for me to place that on the bus and still be able to use all the internal flash including the vector space?

Would it be better and just as fast if I just emulated an addr/data bus on some ports instead?

Basically you have a choice of whether the internal Flash is available or not in expanded mode (see the ROMON and ROMCTL descriptions in your datasheet). Depending on the S12 in use you may have a choice of where the ATD can go in the memory map. Devices with small internal memories have more flexibility with this.

Start with the app note and let us know if you have any more questions.